The present invention relates to a method of recording and reproducing information and an apparatus for recording and reproducing information on and from an optical disk, and in particular, to a method of recording and reproducing information and an apparatus for recording and reproducing information on and from an optical disk using a pit edge recording method suitable for improving a recording density.
A method of demodulation for demodulating recording data by detecting leading edge and a trailing edge of a change in a quantity of a reflected light (i.e. a waveform of a reproduced signal) obtained from an optical disk has been adopted for a digital audio disk (DAD). The principle of the data demodulation is described e.g. in "Introduction to Video Disk and DAD" by Iwamura (Corona Publishing Co. Japan), pp. 212-215. The demodulation is achieved by detecting variation points in the waveform of the reproduction signal, namely, the leading edge and the trailing edge thereof and producing a detection window from the leading edge and the trailing edge so as to attain reproduced data. According to the demodulation method used for the DAD, a correct demodulation is conducted under the conditions that assuming a data interval to be T, the detection window width is T/2 and the pulse representing variation points are located in a region of .+-.T/4. Consequently, an error occurs if a zero cross point (corresponding to a variation point) is moved due to a noise, a waveform distortion, a rotation jitter, an eccentric jitter, etc. to be beyond the detection window. Although the leading edge and the trailing edge can be used as data in an optical disk of a write-once type, since an object disk for the recording and reproducing operations is directly irradiated with laser light pulses to effect a thermal recording thereon in a case of the write-once type disk, the positions of the leading edge and the trailing edge of a recording region (a pit or a magnetic domain) are likely to be easily influenced by a sensitivity characteristic of a recording medium and a jitter consequently, the positions are apt to be indefinitely shifted. In the case of the DAD, since the pits are manufactured in a photoresist forming process when the disk is produced, such a problem has not arisen.
When applying the pit edge recording system to an optical disk of the write-once type or an erasable type, it is essential to correct the edge shift of the leading edge and the trailing edge in any cases during a recording operation.